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Life in 120 Square Feet: Our Solar Power System

So throughout this tour of my tiny house I have described how we live “off the grid” but I haven’t really described exactly how we do that. So, for the penultimate installment of the series, I present to you what it really means for us to live off the grid.

There are two main “systems” that run our tiny house. One is far more technical than the other.

The first, and more technical, is our solar power system. We have two 245 watt panels and a 45 amp Tristar MPPT charge controller. The whole system feeds three 110 amp hour AGM batteries. We have an 1800 watt inverter that converts the energy from DC to AC going into the house. (Some people advocate the use of DC within the house to be more efficient which is true and would be a better solution in many cases.)

Photo By Laura M. LaVoie

Photo By Laura M. LaVoie

Please click or scroll below to read more about our solar system and how it works.

In order to create this system we first determined how much power we would need. We chose to lean toward the side of conservancy. We looked at the very minimum of what we would use electricity for in the house and we designed the system around that. Many people are looking for a solar power system that will run all of the major appliances we are used to in conventional homes but this is what drives the cost up. Anything that converts energy to heat or cold uses a lot of power and will drain the batteries very quickly so a much larger system would be necessary.

Our system runs our laptops for working, Matt’s huge gaming laptop, all of our lights, all of our chargers for devices and batteries, and a Stirling Engine cooler to keep our beer cold; and we usually have power to spare. For situations where it may be raining for days on end we do have a small and efficient Honda generation that we can hook the house, and the batteries, up to.

Photo by Laura M. LaVoie

Photo by Laura M. LaVoie

We worked with an online retailer, the AltE store, to help us put together a system. We knew what we wanted the end result to be but we needed a little guidance from professionals to ensure we had everything to make it happen. All total our solar power system cost us $2000.

Photo by Laura M. LaVoie

Photo by Laura M. LaVoie

You may notice that we built our own mount for the solar panels. We had purchased a “top-of-pole” mount but to be honest, the idea of dragging more concrete up to our mountain had us thinking of alternatives early on. This wooden frame is perfect because we can adjust the angle and even the position of the panels depending on the sun. We really only have to move it twice a year to maximize the sun exposure in the clearing.

Photo by Laura M. LaVoie

Photo by Laura M. LaVoie

Stay tuned later this week for information on our second household system – water.

What kind of solar power system would you design?

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Laura LaVoie

Contributor and Tiny House Owner at 120SquareFeet.com
Laura M. LaVoie is a professional writer living in the mountains of North Carolina in a 120 Square Foot house with her partner and their hairless cat, Piglet. Laura graduated from Western Michigan University with a degree in Anthropology. She has been published in magazines and anthologies on the subjects of mythology and culture. She spent nearly 15 years in the temporary staffing industry before deciding to become a full time writer. Laura works closely with the Zulu Orphan Alliance volunteering her time and the skills she's learned building her own small house to build a shelter for orphans and other vulnerable children living near Durban, KwaZulu-Natal, South Africa. Laura also enjoys simple living, brewing and drinking craft beer, and popular culture.
{ 15 comments… add one }
  • Ralph Sly July 3, 2013, 12:38 pm

    Looking forward to your posts and comments. I want to go solar running DC lighting and the only thing I know about electricity is paying the bill. Need all the help I can get. I have wired a million trailers with lights but this is whole new thing to me. I notice everyone uses 1000 to 1800 watt inverters. I have a 1800 watt and a 3000 watt, would using the 3000 be a benefit going with a solar system. I have been overkill too many times with projects and it has proven more of a detriment than a benefit. I am on hydro and was going to run separate systems but someone said I can tie it into the box here. Running separate does more understand to me, I am not doing anything until I have talked to electricians but want to know some questions to ask? Even the most simple advice is welcome with the level of my understanding of this project.

    • Laura M. LaVoie July 4, 2013, 8:15 am

      If you don’t have a large solar set up and large battery bank or a regular need for that much power, it can be a detriment to have a 3000 watt inverter. They all draw current when they’re on even with no load and in general a larger inverter will have a larger draw.

      The hydro system sounds great so it would love to hear more about what you find out.

  • jerryd July 3, 2013, 10:41 pm

    I’m going with 1kw of 24vdc nom PV and a 3kw inverter. I’ll regulate it myself and run the house off 12 at a time, allowing the other to fully charge.

    I won’t be using AGM batteries as overcharge them once to any degree and they die vs flooded which you can refill the water, cost much less, has more kwhr and very robust. Bargaining I got mine for $80 each at a car parts store sold Johnson Control deep cycle batts renamed Duralast. I’m even using them in my EV’s.

    I’ll be running 12vdc to run everything from cooking pots to lights/LED’s to fans, TV, laptop, pumps, etc. About the only thing needing the inverter is my A/C and big power tools. Even most of my power tools are battery powered.

    My 22” TV is a stock one just changed the input cord to replace the outboard power supply.

    I’ve collected various 12v electric frying pan, pots and working on a 12vdc oven using car headlights. They can be found in RV, boating stores.

    My A/C is most important as it gets hot here in Fla. Luckily PV is perfectly suited as there is plenty if you need the A/C.

    I’ll have other power sources like tidal and wind but they are mostly test units I’m going to put into production. Plus my EV’s 4.5kw DC generator used to give them unlimited range rounds it out. I can also use the EV’s battery bank if needed as I did during Hurricane Charley for 3 days.

    • Ralph Sly July 4, 2013, 5:13 am

      Well Jerryd, Your comments on Laura’s post were good for me to take advantage of buzz words (or I should say terminologies) for me to look up and see where all that leads. LOL I for one am going to grab any info on this subject I can.

      I have used many of the DC products you speak about having and didn’t find them as adequate as advertised. Microwaves and the car light oven seemed expensive for what other sources are available for full time use in a residence. But I only used them from the vehicles 2nd battery on the move driving long distances so am by far, not a qualified authority but some of the other and cheaper products like crock pots and water heaters worked pretty well and did a really good job I don’t see them standing up with time.

      I have the opposite problems to really extreme extended heat, and that is the cold. Thank god we don’t worry about Hurricanes and the what-ifs, it’s not too bad where I am but still require full time heat and use quarts bar heaters, they were extremely cheap to run on purchased hydro.

      As for batteries, I was told that AGM batteries hold up a little better in the cold climate than the flooded and have frozen flooded that went dead. Is there nothing available to kick out the charge impute to keep them from over charging? In the same breath, I don’t want to go away and depend on computers much, (its and old guy thing) I do remember a friend changing his 12v batteries to 6v in series and he claimed they held power a lot, and emperies a lot longer than 12v’s. Homer had 2 banks in his RV and I figure more is better so am looking at 3 or possible 4 because I will be consuming more power and using the system many times longer over what he did. I am not satisfied with the 12v recovery on my RV, 4 flooded but use electric power very little and never go on the grid. In the RV I found the solar system far too expensive to purchase than my usage would ever cover but now considering electric refrigeration and heat and electric cooking with lights and I want to really light up the yard, it would be practical.

      Jerry, you indicated you were putting wind system into production, so I figure you must have this technology down a bit so would like, if you have a website, to follow it. I have been trying to figure out what my usage will be and am having a problem doing that so if that is an indication of my ignorance then you know where I am coming form. It may even be that someone like me should stay away from it but I am just to curious.

      • jerryd July 4, 2013, 9:53 pm

        You have to really look for good 12vdc units. I’ll likely modify 120vac ones and run them on 24vdc. But we’ll see how it works out.

        For batteries the 6vdc nom golf cart ones are by far better than 12 units as true deep cycle batteries. They also are about the lowest cost/kwhr, most rugged and easy to care for.

        I like 2 or more banks if possible, using one and charging the other will give you the est life/power/$

        AGM are great batteries but are starved of electrolyte so have less capacity/size and cost 2-5x’s as much as flooded golf cart units.

        You certainly can get charge controllers and you should for both batt types. I just don’t see any reason to waste 2-5x’s the money for little if any benefit.

        Lead batteries should be kept above 60F, below 100f to work right with 70-80f the best. This is not hard as very dense with some insulation under, around the battery box and the small amount of heat from charging, discharging keeps them warm enough.

        Even if they get cold they still work, just at lower level of output down to -20F or so. But they need to be fully charged for that. If almost discharged they could freeze at 28-30F

        Lead batteries can be charged to 14.2vdc at the rate they can discharge so in the 700-1000amp range so if you have to charge by gas, you can do it fast as you can. They like hard charging and can even cool up to 14.2vdc, the gassing point and 80% charge.

        I’m not going to put much up or a website on my wind generator until it’s ready for sale and it’ll take at least a yr of testing once it gets built and I’m on my 34′ trimaran sailboat to mount it on.

        I’m now in an old oak forest with 100% coverage so no wind or solar ;^( Thus a main reason to move back on the water which is about the best RE site you can get. So selling my TH compound here in Tampa Bay and live anchored out where I belong in my 6’x22′ boat cabin.

      • jerryd July 4, 2013, 10:03 pm

        PV has dropped a lot now running under $1/wt or $1k?kw. If you don’t need A/C .5kw should do, even 250wtts if you are conservative.

        I’m buying the power for the rest of my life which $1k/kw does for me. Actually I’ll like get lams, PV without frames at under $.50/wt, anf just build frames and wire them in.

        How much you use you just have to add up. for DC just use amps as volts are the same, 12. Find out how many amps each thing uses x’s how long it’s used for amphrs/day needed and add them all up. Then size the batts for 1-3 days worth and PV for 1.2x’s as much/day. Then use and adjust if needed.

      • Barb D July 4, 2013, 11:36 pm

        I found the solar systems daunting when I first began my quest, too. So I started a folder of ideas & questions I had. I watched alot of solar system how-to YouTube videos, sometimes multiple times, took alot of notes. I got a very affordable off-grid e-book after watching many videos from simplesolarhomesteading.com

        That $7 e-book helped me figure out where to start & how to make an outline of components I’d need based on his descriptions. Admittedly he is self-taught and not held responsible, but I have found his information extremely non-intimidating.

        After I had the outline of components, I went about pricing them online. In the process I learned the differences between different models and what each was for, therefore zeroing in on the precise component I needed for my application.
        I had heard that building your own solar panels was a way to save money, but to make them right it seemed it was going to be as costly or more plus I didn’t need more projects, especially not learning a whole new set of skills.

        Ebay is where I found my monocrystalline solar panels, MLSolar had a set for about $1 per watt but there was a shipping problem to my mountain and I think they were made in China. I ended up going with Renogy Solar – they make their own panels in Louisiana. I ended up with 850 watts for $1100 including shipping which I thought was quite decent. I used Google/Ebay/Craigslist to find best prices on each component separately and ordered them along the way. In the end, I think I did very well gethering my entire system, even down to the cables & connectors. “BatteriesPlus” seems to be the best price to get the 6 pack of generic 6v golf cart batteries I want, online battery shopping is out of the question due to shipping weight/prices. I also don’t want to buy the biggest & best becuz I’ve heard a few nightmare stories of costly mistakes made by rookies, so I figure better cover my basics until I become an expert on this type of system or when it is time to expand. Neither have I purchased the batteries yet, as I am only now beginning construction on my tiny house and I don’t want the batteries to go stale before I’m ready for them.

        Don’t take it from me, I don’t even know if my system will work, but based on the answers from the customer service reps I’ve spoken with at each purchase point along the way, I certainly have a decent grasp of the concepts and I was not afraid to ask for recommendations along the way.

        I found the following quite helpful:
        http://www.backwoodshome.com/articles2/yago116.html
        http://www.simplesolarhomesteading.com
        http://www.12voltbestbuy.com
        http://rimstar.org/renewnrg/mobile_off_grid_solar_power_system.htm

        It’s fun to learn. Take it slow & ask questions!

        • Ralph Sly July 5, 2013, 11:38 am

          Ask and ye shall receive. Thanks Jerryd, Barb and Laura, I found a glossy of terms which is helping me with the terminologies. I do know there is a ton of info out there but it is good to hear from those doing and going through the trials and errors. An effective system is a must for this lifestyle and a little experiment a while ago showed me how expensive it can be if you make judgment mistakes. It didn’t end up costing me but could have. (They took the eq back with no complaints). Jerryd, I will be a reader when you get up and running with your wind concept. I am in a central very small city permanent location and have checked out the vortex benefits of surrounding buildings (to no avail) as I cannot get high enough for a tower so solar it is. Barb, I start a progress, trial and error book on most projects and sure find it helpful, almost becomes a manual when the project is completed and they have come in handy even to remember paint choices. I will also be purchasing PVs for your same reason. Laura, thanks for the post, on your water system post today, good luck, in those examples, I have used a self priming RV pump. I am on municipal water and will continue to use that but for personal use, when hauling water I found I could conserve greatly and intend on doing that for future use. I drain into a bucket and use that water for flushing so I am always reminded of the waste. I may also still use the gravity shower because there is a huge, huge difference in the amount of water I use now compared to a pressure system.

    • Laura M. LaVoie July 4, 2013, 8:10 am

      We’ve not had any problem with AGM batteries and have been using them for four years. The charge controller should mitigate any overcharging issues. The entire system works very well for us.

      It sounds like your batteries are a great solution for you as well.

  • Denny Pugh July 3, 2013, 11:13 pm

    Is the crawlspace underpinned now or are the batteries exposed ? How does the cold weather effect them…..or does it ??

    • Laura M. LaVoie July 4, 2013, 8:19 am

      We don’t have too much of a problem with cold weather here in the south, but last year we traveled during the winter so we put the batteries in a insulated box and stored them in the house. We want to modify the box for use under the house all year round, we just haven’t gotten around to it yet.

      • Denny Pugh July 4, 2013, 12:50 pm

        am in North Carolina s well, in the next couple of I am planning to retire to an off grid tiny house and spend at least winters in or around Boone / Linville area. I am thinking a well insulated cooler would work well for the batteries and was just curious how you handled it. Like the house and of course Piglet.

  • David Ridge July 4, 2013, 1:49 pm

    Currently, in theory, I would prefer to work with a wind turbine to power a TH.

    • jerryd July 4, 2013, 10:14 pm

      Wind generators are nice but whether it’ll work for you depends on your site. You’ll need to get it 20′ at least above most surrounding trees, etc.

      To find more google axial flux wind generator if you want to build your own or Hugh Piggott for more info, basics, advance and free details, plans.

      Buying WG’s is a problem as not that many good ones out there unless you build your own thus why I’m going into production to fill that void in the market place.

      If you need a smaller one, mine is 14′ dia and 2kw to run a home, the sailboat units of 6-9′ dia along with some PV is a hard combo to beat for a small/tiny home. At the prices they are getting for smaller units, $1k++, I might build that size too .

  • gracemary July 19, 2013, 3:27 pm

    I have the intention of someday living off grid and the solar design mentioned above is what i have in mind for a couple of years now, If it can run my 2 laptops, lights, and and small cooler or better small fridge, the better.

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